Why do some people refuse to fill out group-specific character sheets?

I guess the alternate title to this could be: What is the deal with custom forms?

I am in a roleplay server that has it's own plot, and we have a character template/form specific to our server. This is pretty standard for roleplay servers, in my personal experience. I've just witnessed the third person this month leave our server because they were told they had to fill out our form and could not use their own custom pre-made form. And I just. Do not get why this is a deal-breaker?

But I feel like I'm really lacking context here because I have never used a custom-made form for a character. When I join a new server or forum, I expect them to have made a template for me to fill out w/ my character's info. Even if I'm using a pre-made OC, most templates have a section for stuff like backstory and personality where info can easily be copy-pasted or tweaked to fit the setting. This also streamlines the process of learning about other players' characters, since each form is navigable in the same way (For example: if you're in an RP where every character has a magic ability, you can easily scroll down to the relevant part of any character's form to find what their ability is. It would be in the same section for everyone.)

So, that's my perspective. If you feel differently, please tell me why. What's the appeal? Why would you leave a server over this? I forreal want to know!